Wrap tortillas in aluminum foil and heat in a 350° F oven for 15 minutes. Meanwhile, saute 1 onion in olive oil over medium heat until softened, about 3
minutes. Add rice, pinto beans, and 1 salt and cook for 2 minutes. Stir in
cilantro. Divide the rice-and-bean mixture among the 8 warm tortillas. Top each with some cheese and spinach and roll. Serve with salsa or sour cream, if desired.